Many services on the Internet, such as email, online polls, weblogs, and message boards, are provided free of charge to users. However, these services are particularly vulnerable to abuse because they are free of charge. The abuse often involves malicious users deploying automated scripts or software agents known as bots to use the services in order to send spam, engage in ballot stuffing, and so forth.
Human interaction proofs have been deployed to combat such abuse. Human interaction proofs are used to verify that the user is a human being before granting the user access. An example of a human interaction proof is PIX. PIX involves presenting to the user multiple images of an object and asking the user for a word that identifies the object shown in the images. The images used in PIX may be drawn from an image database or image repository. If the image database is too small, PIX may be subject to attack by memorization. However, gathering and labeling images for an image database can be a time consuming task.
Accordingly, there is a need for a more efficient manner of building a large image repository.